Over the last decade the medical procedure known as angioplasty has become widely accepted as a safe and effective method for treating various types of vascular diseases. For example, angioplasty is widely used for opening stenoses throughout the vascular system and particularly for opening stenoses in coronary arteries. At present, the most common form of angioplasty is called percutaneous transluminal coronary angioplasty (PTCA). This procedure utilizes a dilatation catheter having an inflatable balloon at its distal end. In a procedure using a fluoroscope and radiopaque dyes for visualization the distal end of the dilatation catheter is guided into position through a guide catheter and across the stenosis. With the dilatation balloon in this position of alignment with the stenosis the balloon is inflated for a brief duration to open the artery and establish adequate blood flow.
An alternative procedure for opening blocked or constricted vascular pathways or analogous physical structures utilizes a similar balloon catheter to remove the blockage or embolus by advancing the deflated balloon of the catheter past the blockage, inflating the balloon and then withdrawing the catheter. By withdrawing the inflated balloon the downstream embolus is pulled or stripped from its location and ultimately removed.
Typically, inflation of the balloon is accomplished by supplying pressurized fluid from an inflation apparatus located outside the patient's body through an inflation lumen in the catheter which is connected to the balloon. Conversely, applying a negative pressure to the inflation lumen collapses the balloon to its minimum dimension for initial placement or removal of the balloon catheter within the blood vessel receiving treatment.
In the past years a number of balloon catheter designs have been developed which have contributed to the safety and acceptability of PTCA and similar medical procedures. The most common design is known as an "over-the-wire" balloon catheter. This conventional device typically utilizes a relatively large lumen for passage of a guide wire and injection of contrast fluid (or angiographic visualization dye) to assist in the placement of the device. A second parallel lumen is provided for inflation and deflation of the balloon.
Typically, a steerable guide wire is positioned within the larger lumen and the entire assembly is maneuvered into an initial position within the target artery through a guide catheter which has been positioned previously, and is of sufficient diameter to pass the angioplasty catheter. Once near the site of the stenoses the guide wire can be rotated and axially extended or retracted into position across the lesion. The catheter is subsequently advanced along the guide wire to position its balloon end across the lesion prior to inflation of the balloon and dilation of the stenosis.
Though successful at opening stenotic lesions, these dual lumen catheters are relatively bulky and stiff, which makes their use difficult for any lesions except those that are proximal and localized in nontortuous, easily accessible vessels. Moreover, these over-the-wire balloon catheters of early design require an additional implanting physician or assistant to control the guide wire during positioning of the assembly because catheter and wire movement are independent of one another. This complex coordinated activity requires both experience and skill and may result in a slower insertion procedure than desired.
An alternative conventional over-the-wire catheter assembly utilizes a non-removable guide wire that allows for longitudinal or axial movement. However, this design has a significant drawback because the entire non-removable guide wire catheter assembly must be removed to accomplish replacement or exchange of the balloon. In some cases of PTCA it is necessary to replace the balloon with one of different diameter or configuration following the initial dilation.
Additionally, cases of acute reclosure have been noted where the lesion recloses following dilation and removal of the balloon catheter. One response to this reclosure problem has been the placement of an expandable stent into the artery at the lesion with another replacement balloon catheter. This alternative system increases the difficulties of these subsequent procedures by requiring that the replacement catheter renegotiate the entire placement path without the advantage of a guide wire.
A "monorail" variant of the standard balloon-over-a-wire system also has been developed where only the distal portion of the balloon catheter tracks over the guide wire. This system utilizes a conventional inflation lumen and a relatively short guiding or through lumen at the distal end. Its principal benefits are the reduction of frictional drag over the length of the externally located guide wire and the ease of balloon exchange. It provides the ability to recross an acutely closed vessel or to exchange balloons without removing the guide wire. However, a disadvantage of this "mono-rail" design is the increased difficulty in steering the guide wire because the guide wire is not supported by the balloon catheter. Additionally, the dual lumen distal design produces a larger profile and shaft size.
Another innovation in dilatation catheter design which is now conventional is the "fixed-wire" or integrated "balloon-on-a-wire" dilatation catheter. These single lumen designs utilize a relatively narrow wire positioned within the inflation lumen and permanently fixed to the distal end of the balloon. This construction produces a low-profile catheter assembly which is able to cross severely narrowed lesions and to navigate tortuous vascular pathways. Additionally, the fixed guide wire bonded at the distal end of the balloon improves the steerability and pushability of these designs which enhances their maneuverability. The thin shaft design also improves coronary visualization and enables all but the tightest critical lesions to be crossed.
However, though able to provide relatively quick and simple balloon placement as well as providing access to lesions otherwise unsuitable for PTCA, fixed-wire balloon-on-a-wire systems sacrifice the ability to maintain guide wire position across the lesion when exchanging balloons or the safety advantage of being able to recross an acutely closed vessel without repositioning the entire assembly.
Additionally, conventional dual balloon catheters are known which provide for a pair of dilatation balloons of graduated size, or which provide one balloon which is a dilatation balloon while a second balloon is spaced away from the dilatation balloon. These catheters are used subsequent to the artery dilation with the two balloons both serving as occlusion balloons to isolate a section of the artery including the lesion under treatment between the two inflated balloons. An additional lumen of the catheter communicates with the isolated space between the balloons so the lesion can be treated with therapeutic fluids supplied via this additional lumen. Yet another balloon may be provided in this isolated space to assist in driving the therapeutic material into the tissue of the lesion by pressurizing the isolated intraarterial space or by physically pressing outwardly into engagement with the walls of the artery.
Of course, these conventional multi-lumen, multi-balloon catheters are high-profile devices. That is, the complexity of the structure of the catheter with two or more balloons, and two or more lumens communicating with the balloons and other features of the catheters, results in a rather large diameter for these devices.
Accordingly, it is an object of the present invention to provide a balloon-on-a-wire dilatation or embolectomy catheter which incorporates all of the benefits of a small diameter fixed wire system yet allows for removal, reengagement or replacement of the balloon while leaving the guide wire in place to preserve an easily renegotiated path along the blood vessel being treated.
It is an additional object of the present invention to provide an integrated-wire dilatation or embolectomy catheter offering an extremely low profile and a small shaft size to facilitate maneuverability and placement of the catheter as well as to provide it with the ability to negotiate tortuous vessels and to pass highly stenosed lesions.
It is a further object of the present invention to provide an integrated-wire balloon catheter having a steerable guide wire releasably fixed inside the catheter to provide enhanced torqueability, pushability, and maneuverability in order to facilitate the rapid, single operator placement and positioning of the assembly.
Still additionally, it is an object of the present invention to provide a dual balloon catheter with only a single lumen, and which includes an infusion section intermediate of the two balloons.
Further, it is an object of this invention to provide a single lumen catheter of the type outlined above which includes valving structure responsive to axial movement of the guide wire for selectively allowing inflation of a dilatation balloon, a distal vent to be opened, or inflation of both the dilatation balloon and an occlusion balloon along with infusion of therapeutic material into an isolated space between the two balloons, which material also provides the inflation pressure for the two balloons.